nandi/rustnim · b714bd2

⑂ b714bd2

Count alias substitutions, not descent, against the cycle budget

Making `expand` walk the whole type meant every structural step also charged
against the depth limit, so `Vec<HashMap<String, Vec<..>>>` was reported as a
cyclic alias. A type is a finite tree; only substitution can loop.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

nandithebull committed 2026-09-19T18:12:57-07:00 Browse files

b714bd2 parent: 406427b

modified src/lower.rs +5 -2 Viewed

@@ -1425,7 +1425,10 @@ impl Lowerer {
1425	1425	// outermost node.
1426	1426	use syn::Type;
1427	1427	let mut nested = t.clone();
1428		- let rec = \|me: &Self, e: &syn::Type\| me.expand(e, depth + 1);
	1428	+ // `depth` counts alias substitutions, not descent into the type: a
	1429	+ // deeply nested type is not a cycle, and charging it against the same
	1430	+ // budget made `Vec<HashMap<String, Vec<..>>>` look like one.
	1431	+ let rec = \|me: &Self, e: &syn::Type\| me.expand(e, depth);
1429	1432	match &mut nested {
1430	1433	Type::Reference(r) => {
1431	1434	*r.elem = rec(self, &r.elem)?;
@@ -1482,7 +1485,7 @@ impl Lowerer {
1482	1485	if let syn::PathArguments::AngleBracketed(a) = &mut seg.arguments {
1483	1486	for g in a.args.iter_mut() {
1484	1487	if let GenericArgument::Type(at) = g {
1485		- *at = self.expand(at, depth + 1)?;
	1488	+ *at = self.expand(at, depth)?;
1486	1489	}
1487	1490	}
1488	1491	}

          // outermost node.
          use syn::Type;
          let mut nested = t.clone();
--        let rec = |me: &Self, e: &syn::Type| me.expand(e, depth + 1);
++        // `depth` counts alias substitutions, not descent into the type: a
++        // deeply nested type is not a cycle, and charging it against the same
++        // budget made `Vec<HashMap<String, Vec<..>>>` look like one.
++        let rec = |me: &Self, e: &syn::Type| me.expand(e, depth);
          match &mut nested {
              Type::Reference(r) => {
                  *r.elem = rec(self, &r.elem)?;
                  if let syn::PathArguments::AngleBracketed(a) = &mut seg.arguments {
                      for g in a.args.iter_mut() {
                          if let GenericArgument::Type(at) = g {
--                            *at = self.expand(at, depth + 1)?;
++                            *at = self.expand(at, depth)?;
                          }
                      }
                  }